Passing Data Between View Controllers

Passing data between view controllers is a common requirement in iOS app development. It involves transferring data from one view controller to another, allowing the receiving view controller to access and use that data.

Method 1: Using a Segue

A common way to pass data between view controllers is by using segues. Segues define a transition between two view controllers in a storyboard. Here's how you can do it:

1. Declare a property in the destination view controller to hold the data.

@interface DestinationViewController : UIViewController
@property (nonatomic, strong) NSString *dataToPass;
@end

1. Implement the prepareForSegue:sender: method in the source view controller.

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    if ([segue.identifier isEqualToString:@"mySegue"]) {
        DestinationViewController *destVC = segue.destinationViewController;
        destVC.dataToPass = @"Hello, World!";
    }
}

1. In your storyboard, create a segue between the two view controllers and give it an identifier.

Method 2: Using a Delegate

Another way to pass data between view controllers is by using a delegate. A delegate is an object that acts on behalf of another object.

1. Create a protocol in the source view controller specifying the methods that the delegate should implement.

@protocol DataPassDelegate <NSObject>
- (void)dataDidPass:(NSString *)data;
@end

1. Declare a property in the source view controller to hold a delegate object.

@interface SourceViewController : UIViewController
@property (nonatomic, weak) id<DataPassDelegate> delegate;
@end

1. In the source view controller, call the delegate method to pass the data.

if ([self.delegate respondsToSelector:@selector(dataDidPass:)]) {
    [self.delegate dataDidPass:@"Hello, World!"];
}

1. In the destination view controller, implement the delegate method to receive the data.

- (void)dataDidPass:(NSString *)data {
    NSLog(@"%@", data);
}

Method 3: Using Singleton

A third approach to passing data between view controllers is by using a singleton. A singleton is a class that allows only one instance of itself to be created.

1. Create a singleton class in which you can store and access the data.

@interface DataManager : NSObject
@property (nonatomic, strong) NSString *data;
+ (instancetype)sharedManager;
@end

@implementation DataManager
+ (instancetype)sharedManager {
    static DataManager *shared = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        shared = [[self alloc] init];
    });
    return shared;
}
@end

1. Set the data in the singleton class in the source view controller.

[[DataManager sharedManager] setData:@"Hello, World!"];

1. Get the data from the singleton class in the destination view controller.

NSString *data = [[DataManager sharedManager] data];
NSLog(@"%@", data);

These are just a few methods to pass data between view controllers in iOS. Each method has its own advantages and use cases, so choose the one that best fits your app's needs.